Cathode ray tube



July 27, 193 7.

M. KNOLL ET AL CATHODE RAY TUBE Filed Aug. 4, 1934 fig, :1

INVENTOR MAX KNOLL" m/rz SCH/Q0751? BY ATTORNEY Patented July 27, 1937 CATHODE BAY TUBE Max Knoll and Fritz Schriiter, Berlin, Germany,

assignors to *lelefunken Gesellschaft Drahtlose Telegraphic m. b. E, Berlin,

many, a corporation of Germany Application August 4, 1934, Serial No. 738,434

In Germany August 2, 1933 6 Claims.

The invention is concerned with a Braun tube which is adapted to the reception of television pictures. It has been suggested to use for this purpose thesame Braun tubes with a gas atmosphere that are employed for oscillographic work.

varied along aline in the picture, sharp picture re-creation, strictly speaking, is feasible only in the presence of a particular value of brightness,

whereas at other brightness values the spot would assume a larger diameter so that no sharp picture could be re-created.

The said shortcoming could be lessened by that gas pressure and maximumstrength of current flowing in the cathode-ray pencil are so tuned oradjusted to each other that for the largest or nearly the largest current of the pencil the luminous spot will be of the smallest diameter. While the increase in the diameter of the spot, tobe sure, will happen also in that case in an undi- 80 minished degree, it will not even to a remote extent make itself so disagreeably felt as before.

Another means to obviate the said drawback inherent in gas-filled television receiver tubes consists in that a magnetic or an electrically acting focussing device is used in addition to a gaseo'us atmosphere having a focussing efiect also.

This insures the advantage that the said increase in the diameter of the spot is lessened inasmuch as the ray-focussing action which is due, to the 40 magnetic or electric focussing means is independent of the strength of the pencil current.

The dependence upon the'current strength of the cathode-ray pencil of the diameter of the spot can-be nearly entirely caused to disappear if the focussing device is controlled at the rhythm or rate of the brightness modulation of the spot. This shall be explained in. what follows by reference to Figs. 1, 2 and 3 of the drawing which refers to three different embodiments of the invention.

In Fig. 1 is illustrated a Braun tube with cathode IO, control cylinder II, anode I2, deflector plate pairs I3, I, and a magnetically acting focussing device, 1. e., a focussing coil I5. Between 55 the control'cylinder II and the cathode I0 is applied the potential serving for. brightness modulation of the spot which is indicated in the drawing by a symbol indicating A. C. between the leads of cathode and control cylinder. The said focussing coil I5 is traversed by a D. C. and by. an A. C: being in synchronism with the brightness modulation, a fact which is indicated in Fig. 1 by a D. C. and an A. C. symbol between the leads brought to the focussing coil. Suppose that the gas pressure and the current flowing through the focussing coil have been so chosen that in the presence of maximum pencil current the spot has the desired minimum diameter. If the voltage at the control cylinder changes in the sense of decreased luminosity, the current of the cathode-ray pencil will experience a. decrease, while the diameter of the spot at the same time will grow. The current of the focussing coil will then increase in order that the small spot diameter occurring in the presence of maximum pencil current may be obtained.

Fig. 2 shows a Braun tube which, contradistinct to that shown in Fig. 1 is furnished with electric focussing means. The latter, comprises three electrodes l6-I8, the central one presenting a positive potential in reference to the two outer ones. The equipotential surfaces of the electrical field generated by the electrode potentials have a shape as roughly shown in Fig. 2 by dotted lines. These equipotential surfaces act upon the p'encil of cathode-rays in the same focussing way as an optical lens of the biconvex type acts upon a pencil of light-rays. The potential difference between the central electrode and the outer ones, as explained in connection with Fig. 1, must grow whenever the brightness of the spot decreases.

It must also be mentionedthat at the middle electrode l1 may be applied a potential that is positive in relation to the outer electrodes l6 and It. This arrangement has also a focussing effectupon the cathocle-rays. Also in this instance the potential difference must grow upon a reduction of the brightness of the spot.

A particularly simple embodiment of the invention is illustrated in Fig. 3 in which only the middle portion of the tube is depicted. The electrodes of the electric focussing device are to be disposed outside the glass wall of the tube and they consist here of annuli Iii-2|. The arrangement of the focussing electrodes without the tube, contradistinct from what is true of high-vacuum tubes, is feasible in the case of gas-filled tubes because in these no, or no appreciable, wall charges are able to form.

The electrodes could-also be fltted directly upon the outside wall of the tube. Electrodes of this kind'are manufactured particularly easily because the outside wall of the tube is sprayed with a metal, preferably with zinc.

We claim: -1'. The method 01? producing luminous 'efiect's in electronic tubes which comprises applying ,1 electrical energy to a control electrode within the 1 10 tube to vary thereby the brilliance of the luminous effects being produced, and electrically com pensating for variances in the size of the luminous areas resulting in accordance with the applied electrical energy.

2. The method of maintaining constant size luminous spots in gas filled cathode ray tubes having a fluorescent end-wall, which comprises a plying to a control electrode system within the 1 tube signalling impulses tending to vary the brilliance of theluminous effects resulting from impact to the cathode ray beam upon the fluorescent end -wall of the tube, and electrically compensating for variances in the size of the resulting luminous spot in accordance with the signalling impulses.

3, An electronic tube of the gas filled type comprising a fluorescent viewing screen, a source of ,electrons for developing under the application of suitable voltages a cathode ray beam, means for controlling the intensity of the cathode ray beam produced, means for supplying signalling impulses to said controlling means, and means energlzed' in accordance with said signalling impulses for compensating for variances in the area of the resulting luminous spot produced by the impingement of the cathode ray 'beam upon the 7 viewing screen.

4. In an electronic device-0f the cathode ray type having contained therein a gas. a source of electrons from which a cathode ray beam is dethe resulting cathode .ra

veloped, a fluorescent area at the end of the device opposite the electron source, means to con trol the resulting cathode ray beam developed within the tube so as to vary thereby the brilliance of the fluorescent efiects produced upon the fluorescent area upon impact to the cathode ray, means for supplying signalling impulses to the control means and electromagnetic means energized by said signalling impulses to compen-y s'ate for variances in area of the luminous effects produced.

5. In an electronic device of the cathode ray type having contained therein a gas, a source oi electrons from which a cathode ray beam is developed, a fluorescent area at the end of the device opposite the electron source, means to control the 7 resulting cathode ray beam developed within the tube so as to vary thereby the brilliance of the fluorescent effects produced upon the fluorescen-t area upon impact to the cathode ray, means 7 for supplying signalling impulses to the control means and electrostatic means energized by said signalling impulses to compensate for variances in area of the luminous efiects produced.

compensate for variances in area. of the )uminous.

efiects produced. 

